This invention relates to phased array antennas, and more particularly, this invention relates to phased array antennas used at millimeter wavelengths.
Microstrip antennas and other phased array antennas used at millimeter wavelengths are designed for use with an antenna housing and a MMIC (millimeter microwave integrated circuit) subsystem assembly used as a beam forming network. The housing can be formed as a waffle-wall array or other module support to support a beam forming network module, which is typically designed orthogonal to any array of antenna elements. Various types of phased array antenna assemblies that could be used for millimeter wavelength monolithic subsystem assemblies are disclosed in U.S. Pat. No. 5,065,123 to Heckaman, the disclosure which is hereby incorporated by reference in its entirety, which teaches a waveguide mode filter and antenna housing. Other microwave chip carrier packages having cover-mounted antenna elements and hermetically sealed waffle-wall or other configured assemblies are disclosed in U.S. Pat. No. 5,023,624 to Heckaman and U.S. Pat. No. 5,218,373 to Heckaman, the disclosures which are hereby incorporated by reference in their entirety. In the ""624 patent, residual inductance of short wire/ribbon bonds to orthogonal beam forming network modules is controlled.
There are certain drawbacks associated with these and other prior art approaches. Above 20 and 30 GHZ, commercially available soft substrate printed wiring board technology does not have the accuracy required for multilayer circular polarized radiation elements, such as quadrature elements. A single feed circular polarized patch antenna element with an integral hidden circular polarized circuitry is desired for current wide scanning millimeter microwave (MMW) phased array applications. Various commercially available soft substrate layers have copper film layers that are thicker than desired for precision millimeter microwave circuit fabrication. Several bondable commercially available soft dielectric substrates have high loss at microwave millimeter wavelengths and the necessary rough dielectric-to-metal interface causes additional attenuation. Many commercially available dielectric substrates are not available in optimum thicknesses. Various dual feed microstrip elements with surface circuit polarized networks have been provided and some with polarizing film covers, but these have not been proven adequate. It would be desirable to minimize the different layers and use microwave integrated circuit materials and fabrication technologies for a phased array antenna with orthogonally positioned beam forming network modules at millimeter microwave wavelengths.
Additionally, the recent trend has been towards higher frequency phased arrays. In Ka-band phased array antenna applications, the interconnect from the element to the beam forming network modules is very difficult to form because the array face is typically orthogonal to the beam forming network modules and any antenna housing support structure.
Fully periodic wide scan phased array antennas require a dense array of antenna elements, such as having a spacing around 0.23 inches, for example, and having many connections and very small geometries. For circular polarized microstrip antennas, there are normally two quadrature feeds required, making the connections even more difficult at these limited dimensions. Some planar interconnects with linear polarization have been suggested, together with a pin feed through a floor if the area allows. Also, any manufacturable, reworkable interconnect that meets high performance requirements for three-dimensional applications with millimeter microwave integrated circuit technology is not available where planar elements must be electrically connected to circuitry positioned orthogonal to elements and meet the microwave frequency performance requirements. Performance must be consistent for each interconnection and the technology must be easily producible and easily assembled where the interconnection must be repairable at high levels of assembly. The technology must also support multiple interconnects over a small area.
The present invention is advantageous and provides a phased array antenna that allows the spacing between a driven antenna element and parasitic antenna element patch antenna elements to be dimensioned for enhanced parasitic antenna element performance of millimeter wavelength signals. The phased array antenna includes an antenna housing having an array face and defining an electrically conductive ground plane layer. A plurality of millimeter wavelength patch antenna elements are positioned on the array face and include a primary substrate having front and rear sides and a driven antenna element positioned on the front side of the primary substrate.
A ground plane layer is positioned on the rear side of the primary substrate and a dielectric layer is positioned on the ground plane layer. A microstrip quadrature-to-circular polarization circuit is positioned on the dielectric layer and a parasitic antenna element layer is positioned forward from the driven antenna element. At least one spacer is positioned between the parasitic antenna element layer and the primary substrate. The spacer is dimensioned for enhanced parasitic antenna element performance at millimeter wavelength signals.
In one aspect of the present invention, the spacer can be formed as precision diameter spaced balls or a peripheral frame structure etched on a dielectric such as bonded glass. The spacer could also be formed as a central support to the parasitic antenna element layer. The primary substrate can be formed from a dielectric material such as glass, including fused quartz, semiconductor substrate such as GaAs, and ceramics such as alumina or beryllia. The parasitic antenna element layer could include a secondary substrate having a parasitic antenna element positioned thereon. The secondary substrate could be formed from a dielectric material. The millimeter wavelength patch antenna elements can be conductively bonded to the array face.
In still another aspect of the present invention, an antenna housing includes a subarray assembly, including a plurality of beam forming network modules supported by the subarray assembly, and an array face defining a ground plane substantially orthogonal to the subarray assembly. A plurality of millimeter wavelength patch antenna elements are positioned on the array face and each associated with a respective beam forming network module. Each patch antenna element includes a primary substrate having front and rear sides.
In another aspect of the present invention, a driven antenna element is positioned on the front side of the primary substrate and a ground plane layer is positioned on the rear side of the primary substrate. A dielectric layer is positioned on the ground plane layer and a microstrip quadrature-to-circular polarization circuit is positioned on the dielectric layer. A parasitic antenna element layer is spaced forward from the driven antenna element and at least one spacer is positioned between the parasitic antenna element layer and the primary substrate. Each spacer is dimensioned for enhanced parasitic antenna element performance at millimeter wavelength radio frequency signals. A single millimeter wavelength feed connects the microstrip quadrature-to-circular polarization circuit with a respective adjacent and orthogonally positioned beam forming network module.
In still another aspect of the present invention, the millimeter wavelength patch antenna element can be placed onto various array faces and includes the primary substrate having front and rear sides and a driven antenna element positioned on the front side of the primary substrate. The ground plane layer is positioned on the rear side of the primary substrate and a dielectric layer is positioned on the ground plane layer. A microstrip quadrature-to-circular polarization circuit is positioned on the dielectric layer and a parasitic antenna element layer is spaced forward from the driven antenna element. At least one spacer is positioned between the parasitic antenna element layer and the primary substrate and the spacer is dimensioned for enhanced parasitic antenna element performance at millimeter wavelength signals.